1. Field of the Invention
This invention relates to transporting viscous hydrocarbon mixtures, e.g. crude oil, by first fractionating the hydrocarbon mixture into at least two fractions, congealing one fraction and then combining the congealed fraction with a more fluid fraction and transporting same preferably in a conduit.
2. Description of the Prior Art
Pumping viscous hydrocarbon mixtures at temperatures below their pour point is very difficult. Heat transfer methods and chemical agents to improve fluid flow properties have been studied. Pour point depressers have been tried as well as diluents to improve the pumpability. Visbreaking agents have also been tried but with little success. In addition, the oil has been congealed, then suspended in water and the combination pumped at temperatures below the pour point of the crude oil.
Examples of patents representative of the art include:
Kells in U.S. Pat. No. 271,080 separates wax from crude oils by pumping the crude oil, e.g. in small streams or jets, into the bottom of a tank containing a brine at a temperature sufficiently low to congeal the wax. The congealed wax is recovered in the brine.
Persch in U.S. Pat. No. 1,154,485 blasts air under pressure into crude oil to form an emulsion of air and oil to increase the fluidity of the oil.
Oberfell et al. in U.S. Pat. No. 2,526,966 teaches transporting viscous crude oils by removing the light hydrocarbons (including straight run gasoline), hydrogenating the residue to increase the fluidity thereof and then combining the hydrogenated product and the light hydrocarbons and pumping the mixture.
Chilton et al. in U.S. Pat. No. 2,821,205 forms a film of water on the interior wall of the pipe to improve the pumpability of viscous oil. A light petroleum or condensed casing-head gas can be admixed with the crude oil to reduce the viscosity.
Scott et al. in U.S. Pat. No. 3,269,401 teach facilitating flow of wax-bearing oil in a pipeline by dissolving therein, at superatmospheric pressure and while above its pour point, a gas such as N.sub.2, CO.sub.2, flue gas, and hydrocarbons containing less than 3 carbon atoms. The "gas becomes associated in some way with the wax crystals and prevents the precipitated wax from agglomerating to form strong wax structures". Also, the gas collects on the surfaces of the wax particles, especially the larger ones, to form films of gas envelopes which isolate the particles from one another and prevent the wax particles from combining.
Kane in U.S. Pat. No. 3,425,429 transports viscous crude oils by forming an oil-in-water emulsion, the water containing a nonionic surfactant.
Watanabe in U.S. Pat. No. 3,468,986 forms spherical particles of wax by melting the wax, then dispersing same in a nonsolvent liquid (e.g. water) maintained at a temperature above the solidification temperature of the wax and thereafter cooling the dispersion to solidify the dispersed droplets into discrete solid particles. The particles can be coated with finely divided solids such as calcium carbonate, etc. Watanabe teaches that it is known in the art to disperse waxy particles by molding, prilling, spray drying, extruding, etc.
Titus in U.S. Pat. No. 3,527,692 transports crushed oil shale in a solvent slurry. The oil shale is first comminuted to a size of 140-325 mesh and then suspended in a solvent such as crude oil, retorted shale oil, or a fraction thereof.
Allen in U.S. Pat. No. 3,548,846 teaches transporting waxy crude oils by incorporating propane or butane within the crude oil.
Vairogs in U.S. Pat. No. 3,618,624 transports viscous crude oils by incorporating a miscible gas, e.g. CO.sub.2, methane, ethane, into the crude to reduce the viscosity thereof.
The art has also used heat, e.g. tracer lines and large heat exchangers placed intermittently along the pipeline, to maintain the crude oil above its pour point and thus facilitate pumping of same. The main disadvantage of these methods is the crude oil tends to "set-up" during shut-downs.
This technology, except for heat transfer systems and crude oil-water suspension systems, has generally proven to be commercially unattractive.